The invention is directed generally to a tape for detecting concealed cable and conduit systems. More particularly, a detectable woven tape is provided having metallic conductors for locating underground dielectric (non-metallic) cable such as fiber optic communications cable.
With increasing use of all dielectric cable in data communications and telecommunications systems, a need exists for reliable and economical methods for detecting dielectric cable, such as fiber optic cable, in underground systems. Such detection methods are needed to reduce the costs typically associated with location and maintenance of dielectric cable and to minimize the disruption in cable communications services.
Prior art detection methods include incorporating a magnetic presence with one or more components of a dielectric cable that does not adversely affect cable performance. For instance, U.S. Pat. No. 5,305,410 discloses incorporating magnetic particles with existing strength members of a cable, and U.S. Pat. No. 5,577,147 discloses use of a polymer matrix layer including magnetic materials to form a detectable layer of a cable sheathing system. Among other prior art detection methods, U.S. Pat. No. 5,017,873 discloses helically wrapping a cable in a magnetic tape including a magnetic powder, or magnetizing a length of a conduit, such that the magnetic tape or magnetized conduit emits a xe2x80x9cmagnetic field signaturexe2x80x9d. The xe2x80x9cmagnetic field signaturexe2x80x9d provides a distinct detection signal that allows an underground dielectric cable to be distinguished from surrounding metallic piping. In addition, as disclosed in U.S. Pat. No. 5,106,175, electronically resonant markers or tags are incorporated with a cable sheathing system for locating a cable by electromagnetic signals.
A disadvantage of prior art magnetic materials is that such materials must be incorporated with cable components during cable manufacturing before installation. Adding magnetic materials to one or more cable components during manufacturing may require additional process steps, increasing production time and manufacturing costs. In addition, prior art magnetic materials as described above do not address the problem of locating previously installed dielectric cable.
Other prior art detection methods include adding a metallic presence to one or more components of dielectric cable. A remote transmitter/receiver is used to locate a buried cable by detecting an electrical signal (field) emitted from a metallic presence on or within the cable as a result of the application of an electrical current to the cable. Copper wire is commonly used as a detector and typically applied to underground dielectric cable as a permanent service cable. Copper wire provides a relatively easy and inexpensive detection method. In such applications, however, copper wire is particularly susceptible to corrosion and lightening strikes due to its relatively exposed nature and, thus, is preferably located within conduits or incorporated with cable components.
To that end, different types of prior art cable tapes including metallic components are applied to dielectric cable to allow detection. For instance, water blocking tape used to wrap insulated optical fibers of dielectric cable may include a metallic conductor, such as a copper conductor, for detection. Also, cable tape used to measure lengths of conduit and to pull cable through innerducts for installation may include a copper conductor to add a metallic presence to dielectric cable.
A disadvantage of prior art tape is the electrical signal (field) that the metallic presence emits is insufficient to locate cable along a long length of conduit. Prior art metallic tapes exhibit low conductivity and high resistance, but cannot reliably locate buried dielectric cable over a long span.
In addition, prior art metallic materials must be applied or incorporated with a dielectric cable or one or more cable components during manufacturing. In the case of metallic (copper) service cables or tracer wires, the cables or wires are applied to a conduit system during installation. Such prior art detection materials do not address the problem of determining the location of existing underground dielectric cable previously installed without a metallic or magnetic presence.
Current methods for locating existing underground dielectric cable for repair and maintenance include exploratory drilling, known as posthole drilling, which is a slow and often costly and unreliable detection method that poses the risks of accidentally damaging or destroying buried cables.
Thus, a detectable tape is needed that includes electrical conductivity and resistance sufficient to help provide reliable and accurate signal detection to locate underground cable over a long distance or a long span of conduit. A detectable tape for use with commercially available detection equipment that provides reliable detection at a wide range of frequencies is required. A detectable tape is needed that is easily applied and not restricted to a method of application to cable.
A detectable woven tape is provided for use in determining a location of an underground cable, e.g., dielectric communications cable. A detectable woven tape is provided having multiple metallic conductors that provide enhanced conductivity and low electrical resistance. The tape provides a highly functional low resistance at a wide range of frequencies to help facilitate accurate and reliable location of an underground dielectric cable over a long distance or a long span of conduit. Low resistance helps permit use of the tape with commercially available equipment to locate cable under different field conditions
The tape has high tensile strength sufficient for use of the tape in other applications, e.g., measuring lengths of conduit and pulling cable through innerducts for installation. The tape is lightweight and flexible, and particularly suited for use in installing and detecting fiber optic communications cable.
In one embodiment, a detectable woven tape comprises a plurality of elongated warp yams grouped into a plurality of substantially parallel bundles. Each bundle includes a certain number of warp yarns. The tape includes three or more elongated metallic conductors, wherein each metallic conductor is substantially parallel to and adjacent one or more bundles. The tape further includes a plurality of elongated weft yarns extending across the bundles and the metallic conductors. Each weft yarn is interlaced with each warp yarn and each metallic conductor. The tape includes at least one elongated fixing yarn arranged substantially perpendicular to the plurality of weft yarns and interlaced with each weft yarn.
Embodiments of the invention may also include one or more of the following features. The metallic conductors are alternately arranged with the bundles. Each weft yarn is substantially equally spaced from and substantially parallel to adjacent weft yarns. Each weft yarn interlaces above every other warp yarn and every other metallic conductor. The warp yarns and the weft yarns are polyester yarns. Each warp yarn and/or each weft yarn includes a denier in a range of from about 1000 to about 4000, and preferably about 2600. The fixing yarn is polyester yarn. The fixing yarn includes a denier in a range of from about 200 to about 1400, and preferably about 840. The warp yarns, the weft yarns and the one fixing yarn include a low coefficient of friction. The low coefficient of friction of the plurality of warp yarns, the plurality of weft yarns and the at least one fixing yarn is in a range of from about 200 to about 1400. The woven tape includes a coating of lubricant.
Embodiments of the invention may further include one or more of the following features. Each metallic conductor includes a gage in a range of from about 15 ga to about 30 ga, and preferably about 22 ga. Each metallic conductor includes a resistance of less than about 5 ohms per 1,000 feet (ohms/mft), or a resistance of from about 4.4 ohms per 1,000 feet (ohms/mft) to about 4.9 ohms/mft. The metallic conductors include copper conductors. The woven tape includes four copper conductors. The woven tape includes a plurality of markings wherein each marking is substantially equally spaced from an adjacent marking indicating a unit of length.